As one of the processes of manufacturing a semiconductor device, a process of forming a nitride film, such as a silicon nitride film (Si3N4 film, hereinafter, also referred to as a SiN film), as a protective film on a substrate with an oxide film, such as a silicon oxide film (SiO2 film, hereinafter, also referred to as a SiO film), formed on a surface thereof may be performed. When an etching process is performed on the substrate, the nitride film formed on the oxide film may be used as an etching stopper or the like to protect the oxide film.
However, when a film thickness of the nitride film is small, the function of the nitride film as a protective film may be degraded. As a result, the oxide film may be damaged when the etching process is performed on the substrate.